Actuator-Assisted Calibration of Freehand 3D Ultrasound System

Figure 1

Principle of freehand 3D ultrasound. Each ultrasound pixel of an ultrasound image () can be expressed with respect to the world coordinate system () by multiplying two transformation matrixes ( and ): , where and are 4 × 4 transformation matrix relating the image coordinate system to the probe coordinate system and the probe coordinate system to the world coordinate system, respectively. Although can be determined from the tracking system, needs to be obtained through probe calibration.